OK, this section should be comparatively short, simple and straightforward compared to the above, but no less important.
The very first thing after a new install you should check the errata notices at http://redhat.com/apps/errata/, and apply all relevant updates. Only a year old you say? That's a long time actually, and not current enough to be safe. Only a few months or few weeks? Check anyway. A day or two? Better safe than sorry. It is quite possible that security updates have been released during the pre-release phase of the development and release cycle. If you can't take this step, disable any publicly accessible services until you can.
Linux distributions are not static entities. They are updated with new, patched packages as the need arises. The updates are just as important as the original installation. Even more so, since they are fixes. Sometimes these updates are bug fixes, but quite often they are security fixes because some hole has been discovered. Such "holes" are immediately known to the cracker community, and they are quick to exploit them on a large scale. Once the hole is known, it is quite simple to get in through it, and there will be many out there looking for it. And Linux developers are also equally quick to provide fixes. Sometimes the same day as the hole has become known.
Keeping all installed packages current with your release is one of the most important steps you can take in maintaining a secure system. It can not be emphasized enough that all installed packages should be kept updated -- not just the ones you use. If this is burdensome, consider uninstalling any unused packages. Actually this is a good idea anyway.
But where to get this information in a timely fashion? There are a number of web sites that offer the latest security news. There are also a number of mailing lists dedicated to this topic. In fact, Redhat has the "watch" list, just for this purpose at https://listman.redhat.com/mailman/listinfo/redhat-watch-list. This is a very low volume list by the way. This is an excellent way to stay abreast of issues effecting your release, and is highly recommended. http://linuxsecurity.com is a good site for Linux only issues. They also have weekly newsletters available: http://www.linuxsecurity.com/general/newsletter.html.
Redhat also has the up2date utility for automatically keeping your system(s) up to date ;-). See the man page for details.
This is not a one time process -- it is ongoing. It is important to stay current. So watch those security notices. And subscribe to that security mailing list today!
It is very simple: make sure your Linux installation is current. Check the Redhat errata for what updated packages may be available. There is nothing wrong with running an older release, just so the packages in it are updated according to what Redhat has made available since the initial release.